In the recent advocation of environmental protection, demand for ceramic honeycomb structures used as catalyst carriers for purification of exhaust gases and others much increases, and as for apparatuses and method for producing them, those apparatuses are used which have attained high productivity by continuous extrusion of the honeycomb structures.
On the other hand, as to the honeycomb structures, attempts have been earnestly made to reduce the heat capacity of cell walls supporting catalysts by reducing the thickness of the cell walls for rapidly raising the catalyst temperature at the time of starting of engine to improve purification performance, and at present a thickness of the cell walls of 0.1–0.2 mm is mainly employed, and in some cell walls a thicknes of less than 0.1 mm is employed. Furthermore, the attempt to thin the cell walls is also made for large-sized honeycomb structures, and at present, large-sized products of more than 150 mm in outer diameter which are thinned in walls are put to practical use.
Under the circumstances, conventional apparatuses for producing honeycomb structures and method for producing them are generally those according to which honeycomb structures extruded from an extruder are continuously extruded in a direction perpendicular to the gravity direction while placing them on a plurality of cradles having concave faces corresponding to the shape of the outer peripheral side face (JP-B-64-6916).
As an automatic cutting device suitable for the apparatuses for producing honeycomb structures and method for producing them by the continuous extrusion molding, there is disclosed an automatic cutting device having a cradle on which the honeycomb structures are placed, a carrying path for moving the cradle with the honeycomb structures placed thereon, a speed sensor for sensing the extruding speed of the honeycomb structures, a cutting device carrying out the cutting of the honeycomb structures while moving in the moving direction of the honeycomb structures at the same speed as the extruding speed of the honeycomb structures which is sensed by the speed sensor (the same patent publication referred to as above).
Furthermore, as the cutting device for cutting the honeycomb structure, small-gage wires made of steel are generally used, and moreover as a cutting device which does not cause distortion of outer walls and cell walls of the honeycomb structures when the small-gage wires are put into the honeycomb structure, there are disclosed a cutting method and an automatic cutting device in which grooves for inducing cutting are provided by a knife or the like on the outer peripheral side surface of the honeycomb structures which is highest in cutting resistance, and the small-gage wires are put in the grooves to cut the honeycomb structures (JP-A-2001-96524).
However, since according to the conventional apparatues and methods, the honeycomb structure is extruded in the direction perpendicular to the gravity direction, there is a problem that its own weight is apt to be applied in the thickness direction of cell wall which is structually small in strength. Therefore, in case a honeycomb structure which is considerably reduced in strength due to the reduction in wall thickness or a honeycomb structure in which its own weight is apt to be applied in the thickness direction of the cell wall due to increase in size is produced, there occurs distortion of outer wall such as rupture, or distortion of cell wall such as cell twisting or mesh creasing owing to its own weight, and these are severe causes to hinder reduction in thickness of walls and increase in size of the honeycomb structure.